Paper substrates incorporating covert marking pigments, and processes for obtaining and using same

ABSTRACT

Paper substrates which incorporate covert marking pigments (CMPs) which are one or more infrared (IR) anti-Stokes pigments. Also, processes for incorporating such CMPs into a paper substrate other than by a printing technique, such as, for example, by using a size press or spraying, as well as processes for identifying the presence of such CMPs incorporated into a paper substrate sheet with an infrared (IR) pigment sensor of, for example, a copier or printer for the purpose of adjusting the quantity of printer pigment deposited on a paper substrate sheet or to determine whether the paper substrate sheet is an authentic or counterfeit document.

FIELD OF THE INVENTION

The present invention broadly relates to paper substrates (includingpaper substrate sheets) which incorporate covert marking pigments (CMPs)which are one or more infrared (IR) anti-Stokes pigments. The presentinvention also broadly relates to processes for incorporating such CMPsinto a paper substrate other than by a printing technique, such as, forexample, by using a size press or spraying. The present inventionfurther broadly relates to processes for identifying the presence ofsuch CMPs incorporated into a paper substrate sheet with an infrared(IR) pigment sensor of, for example, a copier or printer for the purposeof adjusting the quantity of printer pigment deposited on the papersubstrate sheet or to determine whether from the paper substrate sheetis an authentic or counterfeit document.

BACKGROUND

In recent years, the demand for effective “invisible ink” compositionshas steadily increased. “Invisible ink” compositions involve a broadclass of ink formulations with no or minimal visibility to the unaided(naked) eye when applied to, for example, a paper substrate and viewedwith “natural light” (e.g., light from the sun), or light fromconventional lamps or other sources of visible light. These visiblelight forms may be collectively referred to as “white light” whichinvolves a combination of various colored light fractions whichgenerally fall within a wavelength range of, for example, from about 300to about 700 nm. Under these illumination conditions, “invisible ink”compositions are either colorless or virtually colorless. Only afterillumination outside the visible light spectrum do the printed imageswith these “invisible ink” compositions become visible or otherwisedetectible, with or without auxiliary observation equipment such as adetector, sensor, scanner, etc. See U.S. Pat. No. 6,149,719 (Houle),issued Nov. 21, 2000.

The uses of “invisible ink” compositions may vary. For example,“invisible ink” compositions may provide many benefits when printed on avariety of paper substrate documents including insurance policies,checks, etc. For example, invisible ink compositions may be used onpaper substrate documents prepared by financial or investmentinstitutions (e.g., checks, account statements, routing documents,banknotes, stocks, bonds, certificates, vouchers, etc.), by vendorsissuing event admission tickets, by governments issuing identificationpapers such as passports, by manufacturers on packaging, labeling, etc.,of products, etc. Such paper substrate documents may contain a widevariety of routing codes, numerical identifiers, data summaries, etc.,which remain invisible to the unaided eye under “white light,” but whichare revealed when illuminated, sensed, scanned, etc., with other than“white light” to identify whether these paper substrate documents areauthentic or counterfeit, to reveal information, data, etc., present onpaper substrate documents to only certain recipients of such documents,e.g., customers, etc. For example, it may be desired to includebarcoding on such paper substrate documents for inventory control,product assembly applications in factories, etc., where the particularbarcode does not appear in visible form on such products, packaging,labels, etc., being processed. See U.S. Pat. No. 6,149,719 (Houle),issued Nov. 21, 2000.

In addition, banknotes, stocks, bonds, certificates, vouchers, checks,valuable admission tickets and other valuable paper substrate documentssuch as passports and other identity documents may be at risk ofcounterfeiting, as well as product protection elements such as labels,seals, packaging, etc. There are several ways to validate whether suchdocuments are authentic or a counterfeit, ranging from simple tocomplex. Some methods involve hidden (i.e., covert) features which maybe incorporated in such documents, for example, by the use of invisibleink compositions. These covert features may be provided by printingthese invisible ink compositions onto the paper substrate of thedocument in a particular pattern, arrangement, etc. Since these covertfeatures are not detectable, visible, etc., by the human eye, detectors,sensors, scanners, etc., may be used and configured to detect, identify,reveal, etc., these covert features to authenticate such documents. SeeU.S. Pat. No. 6,149,719 (Houle), issued Nov. 21, 2000.

While invisible ink compositions comprise materials with at least someabsorbance of light outside the visible bandwidth, they may also containmaterials which impart visible color (sometimes referred to as“crosstalk”) which may make the invisible ink composition usable onlyunder more limited conditions. For example, one such invisible inkcomposition uses an infrared (IR) ink that absorbs IR light having awavelength of 793 nm and fluorescently emits IR light at a longerwavelength of 840 nm. Because such an ink has a faint green appearance,the ink density may need to be lowered to retain invisibility, but alsomaking the detection of features printed with that ink more difficult.Additionally, both a specialized light source and an imaging device maybe required to detect such inks. Another example of an invisible inkcomposition uses a silicon naphthalocyanine-based IR absorbing ink whichprovides a small light absorption change at a wavelength of 790 nm whichcan be detected by using an illumination source emitting at wavelength790 nm. This smaller IR absorption change is also limited in part byvisible “crosstalk” as this particular ink dye is not truly invisible,but also has a visible green tint. Additionally, “crosstalk” from thevisible ink dye absorption into the IR spectrum may mask or confuse thisweak IR absorption signal. But increasing the IR absorption density toimprove signal detection may be limited because the “crosstalk” invisible absorption region may increase as well. In addition, such IR inkdyes or pigments may be unstable, especially when used in lowerconcentrations, and thus vulnerable to environmental degradation,including high humidity or ink dye fade when exposed to UV or visiblelight. See U.S. Pat. No. 8,941,886 (Kurtz et al.), issued Jan. 27, 2015.

Invisible ultraviolet (UV) inks compositions have also been used such asthose inks in which incident UV light stimulates visible fluorescence.Such UV-stimulated inks are revealed by illumination from specializedlight sources such as black lights or UV LEDs that provide UVA(wavelength of 315-400 nm) or UVB (wavelength of 280-315 nm) light.Because atmospheric filtered solar UV light extends down to a wavelength280 nm, there may be a risk for accidental activation and revealing offeatures when using such ultraviolet (UV) inks. See U.S. Pat. No.8,941,886 (Kurtz et al.), issued Jan. 27, 2015.

SUMMARY

According to a first broad aspect of the present invention, there isprovided a covertly marked paper substrate article comprising:

-   -   a paper substrate; and    -   a covert marking pigment having a particle size in the range of        from about 0.1 to about 5 microns and being incorporated into        the paper substrate in a IR detectable amount in the range of        from about 0.1 to about 1,000 mg/m², the covert marking pigment        being one or more IR anti-Stokes shift pigments selected from        one or more of: yttrium oxide; sodium yttrium fluoride;        lanthanum oxide; lanthanum fluoride; yttrium oxysulfide;        lanthanum oxysulfide; Gadolinium (Gd2O2S); Ytterbium (Yb); or        mixtures thereof.

According to a second broad aspect of the present invention, there isprovided a process for preparing a covertly marked paper substrate, theprocess comprising the following steps:

-   -   (a) providing a composition comprising a covert marking pigment        having a particle size in the range of from about 0.1 to about 5        microns, the covert marking pigment being one or more IR        anti-Stokes shift pigments selected from one or more of: yttrium        oxide; sodium yttrium fluoride; lanthanum oxide; lanthanum        fluoride; yttrium oxysulfide; lanthanum oxysulfide; Gadolinium        (Gd2O2S); Ytterbium (Yb); or mixtures thereof; and    -   (b) incorporating the composition of step (a) by a non-printing        technique into a paper substrate sheet in an IR detectable        amount in the range of from about 0.1 to about 1,000 mg/m².

According to a third broad aspect of the present invention, there isprovided a process for adjusting the amount of printer pigment depositedon a paper substrate sheet, the process comprising the following steps:

-   -   (a) providing a covertly marked paper substrate sheet, the        covertly marked paper substrate sheet comprising:        -   a paper substrate sheet; and        -   a covert marking pigment having a particle size in the range            of from about 0.1 to about 5 microns and being incorporated            into the paper substrate sheet in an IR detectable amount in            the range of from about 0.1 to about 1,000 mg/m² and in a            manner which identifies a type of covertly marked paper            substrate sheet, the covert marking pigment being one or            more IR anti-Stokes shift pigments selected from one or more            of: yttrium oxide; sodium yttrium fluoride; lanthanum oxide;            lanthanum fluoride; yttrium oxysulfide; lanthanum            oxysulfide; Gadolinium (Gd2O2S); Ytterbium (Yb); or mixtures            thereof;    -   (b) scanning the covertly marked paper substrate sheet of        step (a) with an IR pigment sensor to identify the type of        covertly marked paper substrate sheet; and    -   (c) adjusting the quantity of printer pigment deposited on the        of covertly marked paper substrate sheet in response the type of        covertly marked paper substrate sheet identified in step (b).

According to a fourth broad aspect of the present invention, there isprovided a process for determining whether or not a paper substratesheet is an authentic document, the process comprising the followingsteps:

-   -   (a) providing a paper substrate sheet; and    -   (b) scanning the paper substrate sheet with an IR pigment sensor        to detect whether or not the paper substrate sheet incorporates        a specified covert marking pigment, the covert marking pigment        being one or more anti-Stokes shift pigments selected from one        or more of: yttrium oxide; sodium yttrium fluoride; lanthanum        oxide; lanthanum fluoride; yttrium oxysulfide; lanthanum        oxysulfide; Gadolinium (Gd2O2S); Ytterbium (Yb); or mixtures        thereof;        -   wherein if the IR pigment sensor detects that the paper            substrate sheet: (i) does incorporate the specified covert            marking pigment, the paper substrate sheet is identified as            authentic; or (ii) does not incorporate the specified covert            marking pigment, the paper substrate sheet is identified as            counterfeit.

DETAILED DESCRIPTION

It is advantageous to define several terms before describing theinvention. It should be appreciated that the following definitions areused throughout this application.

Definitions

Where the definition of terms departs from the commonly used meaning ofthe term, applicant intends to utilize the definitions provided below,unless specifically indicated.

For purposes of the present invention, the term “covert marking pigment(CMP)” refers to a composition, compound, substance, material, etc.,which is colorless or nearly colorless in the visible light spectrum,but which is visible in the infrared (IR) spectrum. For purposes of thepresent invention the term “specified covert marking pigment” refers toa particular covert marking pigment having a known type of covertmarking pigment for which the IR pigment sensor has been tuned todetect.

For purposes of the present invention, the term “IR anti-Stokes shiftpigment” refers to a CMP which is an up-converting phosphor that absorbslight in the infrared (IR) spectrum, but emits light in the visiblespectrum. Suitable anti-Stokes shift pigments may include, for example,one or more of: yttrium oxide; sodium yttrium fluoride; lanthanum oxide;lanthanum fluoride; yttrium oxysulfide; lanthanum oxysulfide; etc. Theseanti-Stokes shift pigments may also be doped with one or more other rareearth elements such as ytterbium, erbium, thulium, holmium, etc. SeeU.S. Appln. No. 20170369777 (Collins et al.), published Dec. 28, 2017,the entire contents and disclosure of which is herein incorporated byreference, especially paragraphs [0035] through [0037].

For purposes of the present invention, the term “visible light spectrum”refers to the light spectrum having a wavelength in the range of fromabout 400 nm to about 700 nm.

For purposes of the present invention, the term “infrared (IR) spectrum”refers to the light spectrum having a wavelength which is longer thanabout 700 nm and typically in the range of above about 700 nm to about 1mm.

For purposes of the present invention, the term “ultraviolet (UV) lightspectrum” refers to the light spectrum having a wavelength less thanabout 400 nm. The UV light spectrum may be divided into ultraviolet A(UVA) light spectrum (wavelength in the range of from about 315 to about400 nm), the ultraviolet B (UVB) light spectrum (wavelength in the rangeof from about 280 to about 315 nm), and the ultraviolet (UVC) lightspectrum (wavelength in the range of from about 100 to about 280 nm).

For purposes of the present invention, the term “IR detectable amount”refers to an amount of an IR anti-Stokes shift pigment which isdetectable by an IR sensor when incorporated by a non-printing techniqueinto a paper substrate.

For purposes of the present invention, the term “IR pigment sensor”refers to a sensor which can detect the presence of an IR anti-Stokesshift pigment. The IR pigment sensor includes an excitation element thatstimulates and causes the IR anti-Stokes shift pigment to luminescencewithin a particular wavelength range, as well as a detector elementwhich can detect (sense) this luminescence within that wavelength range.The excitation and detector elements may be incorporated as a singlecomponent, or may be separate components but which cooperate together inthe operation of the IR pigment sensor. IR pigment sensor may also be aseparate piece of equipment or may be an attachment for a printer, acopier, a scanner, a multifunctional copier/printer/scanner/faxmachines, etc. Suitable IR pigment sensors may include: NTE3033 InfraredPhotodiodes from NTE Electronics, Inc., Blumfield; NY; RadioShackInfrared LED Emitter and Detector from SparkFun Electronics; GroveInfrared Reflective Sensor v1.2 from Seeed Studio or Arduino; etc.

For purposes of the present invention, the term “non-printing technique”refers to process for incorporating a covert marking pigment (CMP) intoa paper substrate other than by printing the CMP onto a paper substrate.Suitable non-printing techniques for incorporating the CMP into a papersubstrate may include, for example, applying the CMP at the size press,for example, as part of a sizing composition, by spraying the CMP onto apaper substrate; by incorporating into the paper furnish at the wet endof a paper making machine; by curtain coating; by incorporating into thepaper furnish at the head box; by incorporating at other nip points intothe paper furnish; by bonding to the paper fibers; by using the processdisclosed in U.S. Appln. No. 20170037578 (Skaggs et al.), published Feb.9, 2017 (the entire disclosure and contents of which are hereinincorporated by reference) involving separately treating one or bothsurfaces of a paper substrate with an optical brightening agent (OBA)and a multivalent metal salt drying agent, wherein one or both surfacesof the paper substrate is treated with one of these two agents at thesize press, and wherein the surface(s) is treated with the other ofthese two agents before or after the size press, but substituting theCMP in place of the OBA; etc.

For the purposes of the present invention, the term “random” refers to adistribution of the CMP in a manner which is not recognizable (e.g.,repeating) pattern, for example, no regular and/or evening spacing ofCMP distribution, etc.

For the purposes of the present invention, the term “pseudorandom”refers to distribution of the CMP which is in a manner that appears tobe random, but which is not completely random in that there may have insome areas, locations, etc., where the distribution of the CMP may be ina recognizable pattern. For example, the CMP may be sprayed onto thepaper substrate (e.g., by an oscillating jet) where the CMP is appliedas discontinuous spray (and at a lower flow rate) such that the CMP isdistributed in portions of the paper substrate as a recognizablepattern.

For the purposes of the present invention, the term “spectralinterference” refers to those instances where either the lightabsorption spectra and/or the light emittance spectra of two or morephosphors are not sufficiently separated (e.g., there is absorption oremittance spectra overlap) such that there is interference between thosephosphors in terms of absorbing or emitting a particular wavelength or arange of wavelengths of light. In other words, when spectralinterference occurs, the fluorescent materials are competing for thesame wavelength or the same range of wavelengths of light.

For purposes of the present invention, the term “document”(interchangeably referable to as “cards,” or “documentation”) refers toan article comprising one or more paper substrates wherein the papersubstrate(s) incorporating CMPs, and having information printed thereonwhich may be used for purposes of identification, to communicateinformation (e.g., data), to record information (e.g., data), etc.Documents may include, for example, passports, driver's licenses,network access cards, employee badges, visas, immigration documentation,national ID cards, citizenship cards, social security cards, securitybadges, certificates, identification cards, voter registration cards,police ID cards, border crossing cards, legal instruments (e.g.,contracts, wills, trusts, etc.), security clearance badges and cards,gun permits, gift certificates or cards, labels or product packaging,membership cards or badges, etc.

For the purposes of the present invention, the term “authentic” refersto whether the document is genuine, real, valid, bona fide, original,etc.

For the purposes of the present invention, the term “counterfeit” refersto whether the document is a fake, copy, forged, imitation, bogus, etc.

For the purposes of the present invention, the term “paper fibers”refers to any fibrous material which may be used in preparing a fibrouspaper web. Paper making fibers may include pulp (wood) fibers (e.g.,softwood fibers and/or hardwood fibers), kraft fibers (e.g., pulp fibersproduced by the kraft pulping process), as well as wood fibers producedby soda, sulfite, magnetite, cold soda, NSSC, etc., pulp makingprocesses, synthetic fibers, waste paper fibers, recycled paper fibers,fibers from any of hemp, jute, ramie, flax, cotton linters, abaca, woodwaste, straw, bagasse, bamboo, sisal, synthetic (e.g., bicomponent)fibers, etc., as well as any combinations of such fibers.

For the purposes of the present invention, the term “softwood fibers”refers to fibrous pulps derived from the woody substance of coniferoustrees (gymnosperms) such as varieties of fir, spruce, pine, etc., forexample, loblolly pine, slash pine, Colorado spruce, balsam fir, Douglasfir, jack pine, radiata pine, white spruce, lodgepole pine, redwood,etc. North American southern softwoods and northern softwoods may beused to provide softwood fibers, as well as softwoods from other regionsof the world. Inclusion of softwood fibers tends to impart greaterbending stiffness in paper substrates, but also tends to impart rougherand less smooth surfaces in paper substrates, such as those comprisingkraft paper fibers.

For the purposes of the present invention, the term “hardwood fibers”refers to fibrous pulps derived from the woody substance of deciduoustrees (angiosperms) such as birch, oak, beech, maple, eucalyptus,poplars, etc. Inclusion of hardwood fibers in paper substrates tends toimpart smoother surfaces in paper substrates.

For the purposes of the present invention, the term “bleached fibers”refers to paper fibers which have been subjected to a bleaching processto, for example, increase the brightness, whiteness, etc., of the papersubstrate prepared from such fibers.

For the purposes of the present invention, the term “bulk” refers to thevolume or thickness of the paper fibers in relation to their weight.Bulk is the reciprocal of the density (weight per unit volume), and maybe calculated from caliper and basis weight of a paper substratecomprising the paper fibers. Decreasing the bulk (or in other words,increasing the density) of, for example, a paper substrate sheet, causesthat sheet to be smoother, glossier, less opaque, darker, lower instrength, etc. Bulk is measured by TAPPI T-220 method and is reflectedin units of cc/g.

For the purposes of the present invention, the term “optical brighteneragent (OBA)” refers to certain fluorescent materials which may increasethe brightness (e.g., white appearance) of paper substrate surfaces byabsorbing the invisible portion of the light spectrum (e.g., from about340 to about 370 nm) and converting this energy into thelonger-wavelength visible portion of the light spectrum (e.g., fromabout 420 to about 470 nm). In other words, the OBA converts invisibleultraviolet light and re-emits that converted light into blue toblue-violet light region through fluorescence. OBAs may also be referredto interchangeably as fluorescent whitening agents (FWAs) or fluorescentbrightening agents (FBAs). These OBAs may include one or more of:4,4′-bis-(triazinylamino)-stilbene-2,2′-disulfonic acids,4,4′-bis-(triazol-2-yl)stilbene-2,2′-disulfonic acids,4,4′-dibenzofuranyl-biphenyls, 4,4′-(diphenyl)-stilbenes,4,4′-distyryl-biphenyls, 4-phenyl-4′-benzoxazolyl-stilbenes,stilbenzyl-naphthotriazoles, 4-styryl-stilbenes, bis-(benzoxazol-2-yl)derivatives, bis-(benzimidazol-2-yl) derivatives, coumarins,pyrazolines, naphthalimides, triazinyl-pyrenes, 2-styryl-benzoxazole or-naphthoxazoles, benzimidazole-benzofurans or oxanilides, etc, Seecommonly assigned U.S. Pat. No. 7,381,300 (Skaggs et al.), issued Jun.3, 2008, the entire contents and disclosure of which is hereinincorporated by reference. In particular, these OBAs may comprise, forexample, one or more stilbene-based sulfonates (e.g., disulfonates,tetrasulfonates, or hexasulfonates) which may comprise one or twostilbene residues. Illustrative examples of such anionic stilbene-basedsulfonates may include 1,3,5-triazinyl derivatives of4,4′-diaminostilbene-2,2′-disulphonic acid (including salts thereof),and in particular the bistriazinyl derivatives (e.g.,4,4-bis(triazine-2-ylamino)stilbene-2,2′-disulphonic acid), the disodiumsalt of distyrlbiphenyl disulfonic acid, the disodium salt of4,4′-di-triazinylamino-2,2′-di-sulfostilbene, etc. Commerciallyavailable disulfonate, tetrasulfonate and hexasulfonate stilbene-basedOBAs may also be obtained, for example, from Ciba Geigy under thetrademark TINOPAL®, from Clariant under the trademark LEUCOPHOR®, fromLanxess under the trademark BLANKOPHOR®, and from 3V under the trademarkOPTIBLANC®. OBAs may be used in embodiments of the process of thepresent invention in amounts of, for example, from about 0.2 to about 2%by weight of the pulp fibers being bleached, such as from about 0.4 toabout 0.6 by weight of the pulp fibers being bleached.

For the purposes of the present invention, the term “unrefined fibers”refers to pulp fibers which have not been refined, i.e., have not besubjected to a process of mechanical treatment, such as beating, todevelop or modify the pulp fibers, often to increase fiber bondingstrength and/or improve surface properties. See G. A. Smook, Handbookfor Pulp and Paper Technologists (2^(nd) Edition, 1992), page 191-202,the entire contents and disclosure of which is herein incorporated byreference, for a general description of the refining of pulp fibers.

For the purposes of the present invention, the term “CTMP fibers” refersto chemithermomechanical pulp (CTMP) fibers which have subjected to acombination of chemical, thermal, and mechanical treatment. As usedherein, CTMP fibers refer to fibers which have been treated by chemical,thermal, and mechanical treatment in any order of such treatments,including chemi-thermo-mechanical (C-T-M) pulp fibers,thermo-chemi-mechanical (T-C-M) pulp fibers, thermo-mechanical-chemi(T-M-P) pulp fibers, long fiber chemi-mechanical pulp/chemically treatedlong pulp fibers (LFCMP/CTLF), etc. See G. A. Smook, Handbook for Pulpand Paper Technologists (2^(nd) Edition, 1992), pages 60-65, the entirecontents and disclosure of which is herein incorporated by reference,for a general description of chemithermomechanical pulping (CTMP) forpreparing CTMP fibers.

For the purposes of the present invention, the term “bleached CTMPfibers (also referred to interchangeably as “BCTMP fibers” refers tobleached chemithermomechanical pulp (CTMP) fibers which have subjectedto one or more bleaching treatments, bleached chemi-thermo mechanicalpulp (BCTMP) fibers, neutral sulfite semi chemical-pulp (NSSC) fibers,alkaline peroxide mechanical pulp (APMP/AAP) fibers, etc.

For the purposes of the present invention, the term “paper substrate”refers to a fibrous paper web that may be formed, created, produced,etc., from a mixture, furnish, etc., comprising paper fibers, internalsizing agents, etc., plus any other optional papermaking additives suchas, for example, paper fillers, wet-strength agents, optical brighteningagents, etc. The paper substrate may be in the form of a continuousroll, a discrete sheet, etc.

For the purposes of the present invention, the term “paper substratesheet” refers to a discrete sheet of paper substrate.

For the purposes of the present invention, the term “ream” refers to theconventional sense of the term as providing a quantity of printablepaper substrate sheets (e.g., a packaged quantity of printable papersubstrate sheets) in the range of, for example, from about 480 to about516 sheets (e.g., 480, 500 or 516 sheets).

For the purposes of the present invention, the term “printable papersubstrate” refers to any paper substrate which may be printed on with aprinter colorant. Printable paper substrates may include webs, sheets,strips, etc., may be in the form of a continuous roll, a discrete sheet,etc.

For the purposes of the present invention, the term “synthetic fibers”refers to fibers other than wood pulp fibers (e.g., other than pulpfibers) and which may be made from, for example, cellulose acetate,acrylic, polyamides (such as, for example, nylon, etc.) polyacrylics(such as, for example, polyacrylamide, polyacrylonitrile, esters ofmethacrylic acid and acrylic acid, etc.), polyolefins (such as, forexample, polyethylene, polypropylene, etc.), polydienes (such as, forexample, polybutadiene, polyisoprene, polynorbomene, etc.),polyepoxides, polyesters, polyethers (such as, for example, polyethyleneglycol(polyethylene oxide), polybutylene glycol, polypropylene oxide,polyfluorocarbons, etc.

For the purposes of the present invention, the term “bicomponent fibers”refers to synthetic fibers comprising a core and sheath configuration.The core and sheath portions of these bicomponent fibers may be madefrom various polymers. For example, bicomponent fibers may comprise a PE(polyethylene) or modified PE sheath which may have a PET (polyethyleneterephthalate) or PP (polypropylene) core.

For the purposes of the present invention, the term “basis weight,”refers to the grammage of the wood pulp fibers, fibrous web, etc., inthe paper substrate as determined by TAPPI test T410. See G. A. Smook,Handbook for Pulp and Paper Technologists (2n d Edition, 1992), page342, Table 22-11, the entire contents and disclosure of which is hereinincorporated by reference, which describes the physical test formeasuring basis weight. Basis weights used herein are measured in gramsper square meter (gsm) but may also be converted to corresponding basisweights in terms of lbs/1300 ft² or lbs/3000 ft². For example, a basisweight of 75 gsm corresponds to a basis weight of about 20 lbs/1300 ft²or about 46.1 lbs/3000 ft².

For the purposes of the present invention, the term “substrate pigments”refers to mineral pigments (e.g., calcium carbonate, clay (e.g., kaolinclay), talc, etc.), as well as non-mineral materials (e.g., plasticpigments, etc.), which may be used in paper making to reduce materialscost per unit mass of the paper substrate, increase opacity, increasesmoothness, etc. The mineral pigments may be finely divided, forexample, in the size range of from about 0.5 to about 5 microns, may beplaty mineral pigments, etc.

For the purposes of the present invention, the term “calcium carbonate”refers various calcium carbonates which may be used as substratepigments, such as precipitated calcium carbonate (PCC), ground calciumcarbonate (GCC), modified PCC and/or GCC, etc.

For the purposes of the present invention, the term “precipitatedcalcium carbonate (PCC)” refers to a calcium carbonate which may bemanufactured by a precipitation reaction and which may be used as asubstrate (paper) pigment. PCC may comprise almost entirely of thecalcite crystal form of CaCO₃. The calcite crystal may have severaldifferent macroscopic shapes depending on the conditions of production.Precipitated calcium carbonates may be prepared by the carbonation, withcarbon dioxide (CO₂) gas, of an aqueous slurry of calcium hydroxide(“milk of lime”). The starting material for obtaining PCC may compriselimestone, but may also be calcined (i.e., heated to drive off CO₂),thus producing burnt lime, CaO. Water may added to “slake” the lime,with the resulting “milk of lime,” a suspension of Ca(OH)₂, being thenexposed to bubbles of CO₂ gas. Cool temperatures during addition of theCO₂ tend to produce rhombohedral (blocky) PCC particles. Warmertemperatures during addition of the CO₂ tend to produce scalenohedral(rosette-shaped) PCC particles. In either case, the end the reactionoccurs at an optimum pH where the milk of lime has been effectivelyconverted to CaCO₃, and before the concentration of CO₂ becomes highenough to acidify the suspension and cause some of it to redissolve. Incases where the PCC is not continuously agitated or stored for manydays, it may be necessary to add more than a trace of such anionicdispersants as polyphosphates. Wet PCC may have a weak cationiccolloidal charge. By contrast, dried PCC may be similar to most groundCaCO₃ products in having a negative charge, depending on whetherdispersants have been used. The calcium carbonate may be precipitatedfrom an aqueous solution in three different crystal forms: the vateriteform which is thermodynamically unstable, the calcite form which is themost stable and the most abundant in nature, and the aragonite formwhich is metastable under normal ambient conditions of temperature andpressure, but which may convert to calcite at elevated temperatures. Thearagonite form has an orthorhombic shape that crystallizes as long, thinneedles that may be either aggregated or unaggregated. The calcite formmay exist in several different shapes of which the most commonly foundare the rhombohedral shape having crystals that may be either aggregatedor unaggregated and the scalenohedral shape having crystals that aregenerally unaggregated.

For the purposes of the present invention, the term “surface sizecomposition” refers to those compositions (e.g., size presscompositions) which may comprise, for example, surface sizing agents,substrate pigments, multivalent and/or monovalent metal salt dryingagents, cationic dye fixing agents, optical brightening agents (OBAs),solvents, diluents, anti-scratch and mar resistance agents, CMPs, etc.The surface size composition may be formulated as an aqueous solution,an aqueous slurry, a colloidal suspension, a liquid mixture, athixotropic mixture, etc.

For the purposes of the present invention, the term “internal sizing”refers to sizing present in the paper substrate due to internal papersizing agents which are included, added, etc., during the papermakingprocess before a fibrous paper substrate is formed. Internal papersizing agents generally resist penetration of water or other liquidsinto the paper substrate by reacting with the paper substrate to makethe paper substrate more hydrophobic. Illustrative internal paper sizingagents may include, for example, alkyl ketene dimers, alkenyl succinicanhydrides, etc.

For the purposes of the present invention, the term “surface sizing”refers to sizing agents which are applied on, added to, etc., thesurface(s) of the paper substrate. Surface sizing agents generallyresist penetration of water or other liquids into the paper substrate bycovering the paper substrate with a more hydrophobic film. Illustrativesurface sizing agents may include, for example, starch, modified starch,styrene maleic anhydride copolymers, styrene acrylates, polyvinylalcohol (PVOH), etc.

For the purposes of the present invention, the term “surface sizingstarch” refers to surface sizing agents for paper substrates whichcomprise one or more natural starches (i.e., unmodified starchesobtained from plant sources such as maize, wheat, rice, potato, tapioca,etc.) such as cereal starches (e.g., corn starch, wheat starch, ricestarch, potato starch, oat starch, rye starch, barley starch, milletsorghum starch, etc.) and non-cereal starches (e.g., tapioca starch,etc.), modified natural starches (e.g., ethylated starches, oxidizedstarches, such as oxidized corn starch, etc.), or combinations thereof.Modified starches (e.g., oxidized starches such as oxidized corn starch)may be obtained by one or more chemical treatments known in the papersizing starch art, for example, by oxidation to convert some of —CH₂OHgroups to —COOH groups, etc. In some cases the modified starch may havea small proportion of acetyl groups. Alternatively, the starch may bechemically modified to render it cationic (i.e., a cationic starch) oramphoteric (i.e., an amphoteric starch), i.e., with both cationic andanionic charges. The modified starches may also include starchesconverted to a starch ether, or a hydroxyalkylated starch by replacingsome —OH groups with, for example, —OCH₂CH₂OH groups (i.e., ahydroxyethylated starch), —OCH₂CH₃ groups (i.e., an ethylated starch),—OCH₂CH₂CH₂OH groups (i.e., a propylated starch), etc.

For the purposes of the present invention, the term “multivalent metaldrying salt” refers to those metal drying salts wherein the cationicmoiety has a positive charge of two or more (e.g., a calcium cation, amagnesium cation, an aluminum cation, etc.) such as calcium salts,magnesium salts, aluminum salts, etc., and which are water soluble. Thecounter anions for these multivalent metal drying salts may include, forexample, chloride, bromide, acetate, bicarbonate, sulfate, sulfite,nitrate, hydroxide, silicate, chlorohydrate, etc. Suitable multivalentmetal drying salts (e.g., divalent salts, trivalent salts, etc.) mayinclude one or more of calcium chloride, calcium acetate, calciumhydroxide, calcium nitrate, calcium sulfate, calcium sulfite, magnesiumchloride, magnesium acetate, magnesium nitrate, magnesium sulfate,magnesium sulfite, aluminum chloride, aluminum nitrate, aluminumsulfate, aluminum chlorohydrate, sodium aluminum sulfate, vanadiumchloride, etc.

For the purposes of the present invention, the term “monovalent metalsalt drying” refers to those metal drying salts wherein the cationicmoiety is a monovalent cation having a positive charge of one (e.g., asodium cation, a potassium cation, a lithium cation, etc.) such assodium salts, potassium salts, lithium salts, etc. Suitable monovalentmetal drying salts may include one or more of: sodium chloride, sodiumacetate, sodium carbonate, sodium bicarbonate, sodium hydroxide, sodiumsilicates, sodium sulfate, sodium sulfite, sodium nitrate, sodiumbromide, potassium chloride, potassium acetate, potassium carbonate,potassium bicarbonate, potassium hydroxide, potassium silicates,potassium sulfate, potassium sulfite, potassium nitrate, potassiumbromide, lithium chloride, lithium acetate, lithium carbonate, lithiumbicarbonate, lithium hydroxide, lithium silicates, lithium sulfate,lithium sulfite, lithium nitrate, lithium bromide, etc.

For the purposes of the present invention, the term “dry time” refers tothe time it takes for deposited ink to dry on the surface of a printablesubstrate. If the deposited ink does not dry quickly enough, thisdeposited ink may transfer to other printable substrate sheets, which isundesirable. The percentage of ink transferred (“IT %”) is recorded as ameasure of the dry time. The higher the amount of the percentage of inktransferred, the slower (worse) the dry time. Conversely, the lower theamount of the percentage of ink transferred, faster (better) the drytime. In general, embodiments of the printable substrates of the presentinvention provide a percent ink transferred (“IT %”) value equal to orless than about 65%. In some embodiments of the printable substrates ofthe present invention, the IT % value may be equal to or less than about50%, for example, equal to or less than about 40% (e.g., equal to orless than about 30%.

For the purposes of the present invention, the term “solids basis”refers to the weight percentage of each of the respective solidmaterials (e.g., paper pulp fibers, etc.) present in, etc., in theabsence of any liquids (e.g., water). Unless otherwise specified, allpercentages given herein for the solid materials are on a solids basis.

For the purposes of the present invention, the term “solids content”refers to the percentage of non-volatile, non-liquid components (byweight) that are present in the composition, etc.

For the purposes of the present invention, the term “calcium carbonate”refers various calcium carbonates which may be used as paper fillers,such as precipitated calcium carbonate (PCC), ground calcium carbonate(GCC), modified PCC and/or GCC, etc.

For the purposes of the present invention, the term “precipitatedcalcium carbonate (PCC)” refers to a calcium carbonate which may bemanufactured by a precipitation reaction and which may used as a paperfiller. PCC may comprise almost entirely of the calcite crystal form ofCaCO₃. The calcite crystal may have several different macroscopic shapesdepending on the conditions of production. Precipitated calciumcarbonates may be prepared by the carbonation, with carbon dioxide (CO₂)gas, of an aqueous slurry of calcium hydroxide (“milk of lime”). Thestarting material for obtaining PCC may comprise limestone, but may alsobe calcined (i.e., heated to drive off CO₂), thus producing burnt lime,CaO. Water may added to “slake” the lime, with the resulting “milk oflime,” a suspension of Ca(OH)₂, being then exposed to bubbles of CO₂gas. Cool temperatures during addition of the CO₂ tend to producerhombohedral (blocky) PCC particles. Warmer temperatures during additionof the CO₂ tend to produce scalenohedral (rosette-shaped) PCC particles.In either case, the end the reaction occurs at an optimum pH where themilk of lime has been effectively converted to CaCO₃, and before theconcentration of CO₂ becomes high enough to acidify the suspension andcause some of it to redissolve. In cases where the PCC is notcontinuously agitated or stored for many days, it may be necessary toadd more than a trace of such anionic dispersants as polyphosphates. WetPCC may have a weak cationic colloidal charge. By contrast, dried PCCmay be similar to most ground CaCO₃ products in having a negativecharge, depending on whether dispersants have been used. The calciumcarbonate may be precipitated from an aqueous solution in threedifferent crystal forms: the vaterite form which is thermodynamicallyunstable, the calcite form which is the most stable and the mostabundant in nature, and the aragonite form which is metastable undernormal ambient conditions of temperature and pressure, but which mayconvert to calcite at elevated temperatures. The aragonite form has anorthorhombic shape that crystallizes as long, thin needles that may beeither aggregated or unaggregated. The calcite form may exist in severaldifferent shapes of which the most commonly found are the rhombohedralshape having crystals that may be either aggregated or unaggregated andthe scalenohedral shape having crystals that are generally unaggregated.

For the purposes of the present invention, the term “brightness” refersto the diffuse reflectivity of paper, for example, at a mean wavelengthof light of 457 nm. As used herein, brightness of the paper substratemay be measured in terms of ISO Brightness which measures brightnessusing, for example, an ELREPHO Datacolor 450 spectrophotometer,according to test method ISO 2470-1, using a C illuminant with UVincluded.

For the purpose of the present invention, the term “printer” refers toany device which prints an image on a printable substrate, such as apaper sheet, including laser printers, inkjet printers,electrophotographic recording devices (e.g., copiers), scanners, faxmachines, etc.

For the purpose of the present invention, the term “printer pigment” mayrefer to either ink (as used by, for example, an inkjet printer, etc.)and toner (as used by, for example, a laser printer, electrographicrecording device, etc.).

For the purpose of the present invention, the term “ink” refers toprinter pigment as used by ink jet printers. The term ink may includedye-based inks and/or pigment-based inks. Dye-based inks comprise a dyewhich may be an organic molecule which is soluble in the ink medium.Dye-based inks may be classified by their usage, such as acid dyes,basic dyes, or direct dyes, or by their chemical structure, such as azodyes, which are based on the based on an —N═N— azo structure; diazoniumdyes, based on diazonium salts; quinone-imine dyes, which are derivatesof quinine, etc. Pigment-based inks comprise a pigment, which is a solidcolored particle suspended in the ink medium. The particle may comprisea colored mineral, a precipitated dye, a precipitated dye which isattached to a carrier particle, etc. Inks are often dispensed,deposited, sprayed, etc., on a printable medium in the form of dropletswhich then dry on the printable medium to form the print image(s).

For the purpose of the present invention, the term “toner” refers toprinter pigment (including toner resins) as used by laser printers.Toner is often dispensed, deposited, etc., on the printable medium inthe form of particles, with the particles then being fused on theprintable medium to form the image.

For the purposes of the present invention, the term “flooded nip sizepress” refers to a size press having a flooded nip (pond), also referredto as a “puddle size press.” Flooded nip size presses may includevertical size presses, horizontal size presses, etc.

For the purposes of the present invention, the term “metering sizepress” refers to a size press that includes a component for spreading,metering, etc., deposited, applied, etc., a surface size composition ona paper substrate side or surface. Metering size presses may include arod metering size press, a gated roll metering size press, a doctorblade metering size press, etc.

For the purposes of the present invention, the term “rod metering sizepress” refers to metering size press that uses a rod to spread, meter,etc., the surface size composition on the paper substrate surface. Therod may be stationary or movable relative to the paper substrate.

For the purposes of the present invention, the term “gated roll meteringsize press” refers to a metering size press that may use a gated roll,transfer roll, soft applicator roll, etc. The gated roll, transfer roll,soft applicator roll, etc., may be stationery relative to the papersubstrate, may rotate relative to the paper substrate, etc.

For the purposes of the present invention, the term “room temperature”refers to the commonly accepted meaning of room temperature, i.e., anambient temperature of 20° to 25° C.

For the purposes of the present invention, the term “comprising” meansvarious compounds, components, polymers, ingredients, substances,materials, layers, steps, etc., may be conjointly employed inembodiments of the present invention. Accordingly, the term “comprising”encompasses the more restrictive terms “consisting essentially of” and“consisting of.”

For the purposes of the present invention, the term “and/or” means thatone or more of the various compositions, compounds, polymers,ingredients, components, elements, capabilities, layers, steps, etc.,may be employed in embodiments of the present invention.

DESCRIPTION

For covert marking pigment (CMP) compositions, infrared (IR) absorptiveinks and infrared (IR) sensors may be used to track and authenticate anumber of different types of documents, including, for example, labels,barcodes, other identifiable markings formed by these IR absorptive inkson the surface of such documents, etc. Once marked, such documents maythen be illuminated with IR light and examined by an infrared sensor toauthenticate or track the document. Even so, prior IR dyes used in suchinks may have associated visible color to them, causing the resultingdye-based IR inks and the printed matter to be visibly colored.Additionally, prior dye-based IR inks have traditionally suffered fromlimited solubility in the ink base and low light fastness andenvironmental fastness (e.g., air, water, humidity, thermal fastness,etc.). Further, traditional pigmented IR absorptive inks may includecarbon black as the IR absorptive material, resulting in a dark andhighly visible ink. Such visibility and potential discoloration issuesmakes these prior dye-based IR inks problematical when used with, forexample, white-tinted paper substrates.

To avoid such visible coloring on white-tinted paper substrates,infrared (IR) anti-Stokes shift pigments may be used as the covertmarking pigment (CMP) in these CMP compositions. But in order to includesuch CMPs, the IR anti-Stokes shift pigment may need to be ground veryfinely to be compatible with the vehicle used in the CMP composition fordispersing the pigment. Such grinding of these pigments may greatlyincrease the cost of using them per kilogram of such CMP compositionsused. Alternatively, these IR anti-Stokes shift pigments may requiresurface treatment to be compatible with the ink vehicle so that thisvehicle may wet and retain the pigment particles, also adding to thecost of the CMP composition. To be printed onto a paper substrate, suchCMP compositions comprising these IR anti-Stokes shift pigments mayrequire a variety of other chemical components (e.g., viscositymodifiers, dispersants, solvents, binders, etc.) to enable the CMPcompositions to be printed, to dry and to retain such IR anti-Stokesshift pigments once dried, all of which again add to cost of using theseCMP compositions.

In addition, when printing such a CMP composition onto a papersubstrate, the IR anti-Stokes shift pigment may need to be printed in aparticular location or spot on the paper substrate. That also means thatthe sensor for the IR anti-Stokes shift pigment may need to beinstructed where to look for that pigment. That may be particularly truewhere the CMP composition is printed onto a paper substrate for thepurpose of permitting authentication of the document, such as, forexample, banknotes, clothing tags, tickets, badges, etc.

In response to these visibility, cost, etc., issues, embodimentsaccording to the present invention provide covertly marked papersubstrate articles which include a paper substrate and a covert markingpigment (hereafter referred to as “CMP”). The CMP has a particle size inthe range of from about 0.1 to about 5 microns. This range includes allvalues and subranges therebetween, including 0.1, 0.2, 0.3, 0.4, 0.5,0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9,2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3,3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7,4.8, 4.9, and 5.0 microns. The CMP is incorporated into the papersubstrate in a IR detectable amount in the range of from about 0.1 toabout 1,000 mg/m² (such as from about 2 to about 10 mg/m²). This rangeincludes all values and subranges therebetween, including 0.1, 0.2, 0.3,0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7,1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1,3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5,4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0,6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4,7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8,8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 10, 50, 100, 150,200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850,900, 950, and 1000 mg/m². The CMP can be one or more IR anti-Stokesshift pigments selected from one or more of: yttrium oxide; sodiumyttrium fluoride; lanthanum oxide; lanthanum fluoride; yttriumoxysulfide; lanthanum oxysulfide; Gadolinium (Gd2O2S); Ytterbium (Yb);or mixtures thereof.

Embodiments of the present invention also relate to a process forpreparing these covertly marked paper substrates. The process includesthe step of providing a composition comprising a CMP having a particlesize in the range of from about 0.1 to about 5 microns, the CMP beingone or more IR anti-Stokes shift pigments selected from one or more of:yttrium oxide; sodium yttrium fluoride; lanthanum oxide; lanthanumfluoride; yttrium oxysulfide; lanthanum oxysulfide; Gadolinium (Gd2O2S);Ytterbium (Yb); or mixtures thereof. The process also includes the stepof incorporating the composition of step (a) by a non-printing techniqueinto a paper substrate in a IR detectable amount in the range of fromabout 0.1 to about 1,000 mg/m² (such as from about 2 to about 10 mg/m²).This range includes all values and subranges therebetween, including0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4,1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8,2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2,4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.6, 5.7,5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1,7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5,8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9,10, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700,750, 800, 850, 900, 950, and 1000 mg/m².

Embodiments of the present invention further relate to a process foradjusting the amount of printer pigment deposited on a paper substratesheet by providing a covertly marked paper substrate sheet comprising: apaper substrate sheet; and a CMP having a particle size in the range offrom about 0.1 to about 5 microns, and being incorporated into the papersubstrate sheet in an IR detectable amount in the range of from about0.1 to about 1,000 mg/m² (such as from about 2 to about 10 mg/m²) and ina manner which identifies a type of covertly marked paper substratesheet, the covert marking pigment being one or more anti-Stokes shiftpigments selected from one or more of: yttrium oxide; sodium yttriumfluoride; lanthanum oxide; lanthanum fluoride; yttrium oxysulfide;lanthanum oxysulfide; Gadolinium (Gd2O2S); Ytterbium (Yb); or mixturesthereof. These ranges include all values and subranges therebetween,including 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2,1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6,2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0,4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, and 5.0 microns and 0.1,0.2, 0.3, 0.4, 0.5, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6,1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0,3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4,4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8,5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2,7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6,8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 10, 50,100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750,800, 850, 900, 950, and 1000 mg/m², respectively. In this process, thecovertly marked paper substrate sheet is scanned with an IR pigmentsensor to identify the type of covertly marked paper substrate sheet.The quantity of printer pigment deposited on the covertly marked papersubstrate sheet is adjusted in response to the type of covertly markedpaper substrate sheet identified by the IR pigment sensor.

Embodiments of the present invention further relate to a process fordetermining whether or not a paper substrate sheet is an authenticdocument. In this process, the paper substrate sheet is also scannedwith an IR pigment sensor but to detect whether or the paper substratesheet incorporates a specified CMP, the CMP being one or more IRanti-Stokes shift pigments selected from one or more of: yttrium oxide;sodium yttrium fluoride; lanthanum oxide; lanthanum fluoride; yttriumoxysulfide; lanthanum oxysulfide; Gadolinium (Gd2O2S); Ytterbium (Yb);or mixtures thereof. If the IR pigment sensor detects that the papersubstrate sheet does incorporate the specified CMP, the paper substratesheet is identified as authentic. Conversely, if the IR pigment sensordetects that the paper substrate sheet does not incorporate thespecified CMP, the paper substrate sheet is identified as counterfeit.

Embodiments of the covertly marked paper substrate (including sheets orreams of such covertly marked paper substrates) according to the presentinvention thus contain a CMP which is invisible to the naked eye underconditions of illumination by white light. As such, copiers, printers,multifunctional copier/printer/scanner/fax machines, etc., may beequipped with IR sensors to identify the type paper substrate sheetwhich has the covert marking pigment, and thus may adjust (e.g., reduce)the quantity of toner or ink required to produce a suitable image.Embodiments of the covertly marked paper substrate sheet according tothe present invention which contain the CMP may also be used todetermine whether from the paper substrate sheet it is an authentic orcounterfeit document. In addition, by incorporating the CMP into thepaper substrate by other than a printing technique, such as by applyingthe CMP composition at the size press or by spraying it onto the papersubstrate sheet, a larger particle size of CMP may can be used. Suchlarger particle sizes of CMP may reduce the cost of the CMPcompositions, including reducing the cost of how much of the surfacearea of the substrate needs to be treated with the CMP to be detectableby an IR sensor. In some embodiments, the CMPs, if compatible, may beincorporated as a component of the size press composition. In otherembodiments, the CMPs may be incorporated by: spraying the CMP onto apaper substrate; by incorporating the CMP into the paper furnish at thewet end of a paper making machine; by curtain coating the CMPcomposition; by incorporating the CMP into the paper furnish at the headbox; by incorporating the CMP at other nip points into the paperfurnish; by bonding the CMP to the paper fibers in the paper furnish;etc.

The CMPs used in such of the CMP compositions may be selected tominimize, avoid, etc., spectral interference with the optical propertiesof the paper substrate sheet, including such sheets which incorporate,for example, optical brightening agents (OBAs), other paper pigments,especially those imparting a white tint, etc. In other words, the papersubstrate sheet treated with the CMP compositions may maintain thedesired optical properties in the visible spectrum as if CMP compositionwere absent, i.e., the CMPs and composition comprising same should beselected so as to not cause spectral interference with the fluorescenceof OBAs, etc., which may be used in such paper substrate sheets. Otherfactors for selecting suitable CMPs may include adverse impacts on theelectrostatic properties (resistance, capacitance, etc) of the paperwhich may be needed, for example, for xerographic copying, whether theCMPs might include hazardous materials, such as heavy metals, which arenot toxicologically safe to use with paper substrates, whether the CMPsmight adversely impact the shade/color/tint of the paper substrate,whether the CMPs are thermally stable, etc.

In embodiments of processes according to the present invention, the CMPmay be distributed in a random pattern, pseudo-random pattern, etc. Suchpatterns of distribution of the CMP may permit minimizing the amount ofCMP incorporated per unit of paper substrate surface, i.e., in terms ofmg/m². The CMP composition may be applied to both outer surfaces of thepaper substrate, but may also be applied to only one outer surface ofthe paper substrate. The CMP composition may also be incorporated belowthe outer surfaces of the paper substrate depending upon the penetratingpower of the wavelength that the IR sensor uses. The ability to use IRsensors having wavelengths with increased penetration of the CMP-treatedsheet may also permit inclusion of lesser amounts of CMP in the papersubstrate sheet.

In some embodiments of the present invention for adjusting ink or tonerusage, the IR sensor of the printer, copier, multifunctionalcopier/printer/scanner/fax machines, etc. may be tuned to inspect eachsuch paper substrate sheet, and to initiate and retain a lower ink ortoner usage setting for a specified number of such paper substratesheets. For example, in some embodiments in the form of a ream of papersubstrate sheets, only a portion of the paper substrate sheets aretreated with the CMP composition. In these embodiments, only some butnot all of a specified number paper substrate sheets of the ream havebeen treated with the CMP composition. For example, the ream may combinepaper substrate sheets such that only a portion (i.e., a specifiednumber) of the paper substrate sheets have been treated with the CMPcomposition. For example, in some embodiments, from one in three to onein five paper substrate sheets of the ream may be treated with the CMPcomposition. Such an embodiment would also permit using and combiningdifferent rolls of paper substrate wherein, for example, only one of therolls of paper substrate has been treated with the CMP composition. Sucha multi-roll embodiment may reduce the amount of CMP compositionrequired, and thus again reduce the additional cost imparted by theCMP-treated paper substrate sheet. In an alternative embodiment, onlythe edge of the paper substrate roll may be treated with the CMPcomposition, for example, by a spraying the CMP composition onto theedge of the roll of paper substrate. In yet another alternativeembodiment, a plurality of paper substrate sheets in the form of, forexample, a ream may have one edge of the paper substrate sheets in thatream treated with the CMP composition. In such an embodiment, the IRsensor of the printer, copier, multifunctionalcopier/printer/scanner/fax machines, etc, may be instructed to scan theedge of the ream or partial ream of paper substrate sheets in the trayof the printer, copier, multifunctional copier/printer/scanner/faxmachines, etc, to determine the type of paper substrate sheet in thetray and to adjust the ink or toner usage accordingly.

EXAMPLES Example 1

Paper that had not been treated in a size press was prepared. A sizepress solution was prepared with starch and the following additivescalcium carbonate, sodium chloride and optical brightening agents. Thestarch solids were adjusted to simulate the starch pick on a productionpaper machine tonnage targeting 120 pounds per ton total starch pickup.The taggant was added to the starch and applied in surface starch usingthe sheet fed size applicator. Two taggants used were IR absorbing withgreen visible light emission (GO) and IR absorbing invisible emission(10). Loading for each taggant was 25, 50 and 100 ppm based upon papertonnage targeting 120 pounds per ton total starch pickup.

Conditions: The sheet was weighed before applying the starch. After thestarch was applied to the sheet, the wet sheet was then dried and thestarch pickup was measured. Control sheets were run without CMPs.Different concentrations of CMP in the size press solution were appliedto both sides of the sheet. The example sheets were illuminated and thefluorescent response was measured at 950 nm. The sheets showed anincrease in IR emission as the PPM of taggant was increased.

TABLE 1 CMP Loading CMP Loading (ppm) (mg/m²) CMP1 CMP2 0 0 87 87 25 2.2111 109 50 4.4 127 121 100 8.9 158 130

Example 2

The same procedure was followed as in Example 1, but starch solutionwith CMP was applied to only one side of the sheet. The other side ofthe sheet had only starch solution applied.

TABLE 2 CMP CMP CMP1 CMP1 CMP2 CMP2 Loading Loading Untreated TreatedUntreated Treated (ppm) (mg/m²) side side side side 0 0 87 87 87 87 252.2 98 103 95 114 50 4.4 100 111 103 114 100 8.9 127 139 not run 135

All documents, patents, journal articles and other materials cited inthe present application are hereby incorporated by reference.

Although the present invention has been fully described in conjunctionwith several embodiments thereof with reference to the accompanyingdrawings, it is to be understood that various changes and modificationsmay be apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims, unless they departtherefrom.

What is claimed is:
 1. A covertly marked paper substrate articlecomprising: a paper substrate; and a covert marking pigment having aparticle size in the range of from about 0.1 to about 5 microns andbeing incorporated into the paper substrate in an IR detectable amountof from about 0.1 to about 1,000 mg/m², the covert marking pigment beingone or more IR anti-Stokes shift pigments selected from one or more of:yttrium oxide; sodium yttrium fluoride; lanthanum oxide; lanthanumfluoride; yttrium oxysulfide; lanthanum oxysulfide; Gadolinium (Gd2O2S);Ytterbium (Yb); or mixtures thereof.
 2. The article of claim 1, whereinthe covert marking pigment has a particle size in the range of fromabout 0.5 to about 1.5 microns.
 3. The article of claim 1, wherein thecovert marking pigment is incorporated into the paper substrate in an IRdetectable amount of from about 2 to about 10 mg/m².
 4. The article ofclaim 1, wherein the IR anti-Stokes shift pigments are selected from oneor more of: yttrium oxide; sodium yttrium fluoride; lanthanum oxide;Gadolinium (Gd2O2S); or Ytterbium (Yb).
 5. The article of claim 1,wherein the covert marking pigment is distributed randomly in the papersubstrate.
 6. The article of claim 1, wherein the paper substrate hastwo outer surfaces and wherein the covert marking pigment is applied toone of the two outer surfaces.
 7. The article of claim 1, wherein thepaper substrate has two outer surfaces and wherein the covert markingpigment is incorporated below the two outer surfaces.
 8. The article ofclaim 1, which is in the form of a ream of paper substrate sheets, atleast a portion of the ream comprising covertly marked paper substratesheets.
 9. The article of claim 8, wherein the covertly marked papersubstrate sheets in the ream comprise from one in three to from one infive paper substrate sheets in the ream.
 10. The article of claim 8,wherein the paper substrate sheets have two opposed side edges, andwherein the covert marking pigment is incorporated on one of the sideedges of each covertly marked paper substrate sheet in the ream.
 11. Thearticle of claim 1, wherein the paper substrate includes an opticalbrightening agent.
 12. A process for preparing a covertly marked papersubstrate, the process comprising the following steps: (a) providing acomposition having a covert marking pigment having a particle size inthe range of from about 0.1 to about 5 microns, the covert markingpigment being one or more IR anti-Stokes shift pigments selected fromone or more of: yttrium oxide; sodium yttrium fluoride; lanthanum oxide;lanthanum fluoride; yttrium oxysulfide; lanthanum oxysulfide; Gadolinium(Gd2O2S); Ytterbium (Yb); or mixtures thereof; and (b) incorporating thecomposition of step (a) by a non-printing technique into a papersubstrate in an IR detectable amount of from about 0.1 to about 1,000mg/m².
 13. The process of claim 12, wherein the composition of step (a)comprises a size press composition which further comprises a sizingagent, and wherein the size press composition is incorporated into thepaper substrate in step (b) at a size press.
 14. The process of claim12, wherein the covert marking pigment of step (a) has a particle sizein the range of from about 0.5 to about 1.5 microns.
 15. The process ofclaim 12, wherein the covert marking pigment is incorporated into thepaper substrate during step (b) in an IR detectable amount of from about2 to about 10 mg/m².
 16. The process of claim 12, wherein the IRanti-Stokes shift pigments of step (a) are selected from one or more of:yttrium oxide; sodium yttrium fluoride; lanthanum oxide; Gadolinium(Gd2O2S); or Ytterbium (Yb).
 17. The process of claim 12, wherein step(b) is carried out by randomly distributing the covert marking pigmentin the paper substrate.
 18. The process of claim 12, wherein the papersubstrate of step (b) has two outer surfaces and wherein the covertmarking pigment is applied to one of the two outer surfaces during step(b).
 19. The process of claim 12, wherein the paper substrate of step(b) is formed into a ream of paper substrate sheets, and wherein fromone in three to from one in five paper substrate sheets in the ream arecovertly marked paper substrate sheets.
 20. The process of claim 19,wherein the paper substrate of step (b) has two opposed side edges, andwherein the covert marking pigment is incorporated on one of the sideedges of each covertly marked paper substrate sheet in the ream.
 21. Aprocess for adjusting the amount of printer pigment deposited on a papersubstrate sheet, the process comprising the following steps: (a)providing a covertly marked paper substrate sheet, the covertly markedpaper substrate sheet comprising: a paper substrate sheet; and a covertmarking pigment having a particle size in the range of from about 0.1 toabout 5 microns and being incorporated into the paper substrate sheet inan IR detectable amount of from about 0.1 to about 1,000 mg/m² and in amanner which identifies a type of covertly marked paper substrate sheet,the covert marking pigment being one or more IR anti-Stokes shiftpigments selected from one or more of: yttrium oxide; sodium yttriumfluoride; lanthanum oxide; lanthanum fluoride; yttrium oxysulfide;lanthanum oxysulfide; Gadolinium (Gd2O2S); Ytterbium (Yb); or mixturesthereof; and (b) scanning a paper substrate sheet with an IR pigmentsensor to adjust the quantity of printer pigment deposited on thecovertly marked paper substrate sheet in response to identify the typeof covertly marked paper substrate sheet; and (c) adjusting the quantityof printer pigment deposited on the covertly marked paper substratesheet in response to the type of covertly marked paper substrate sheetidentified in step (b).
 22. The process of claim 21, wherein the papersubstrate sheet of step (a) has two outer surfaces and wherein thecovert marking pigment is applied to one of the two outer surfaces, andwherein the IR pigment sensor of step (b) scans the outer surfaces ofeach of the paper substrate sheets of step (a).
 23. The process of claim21, wherein each paper substrate sheet of step (a) has two opposed sideedges, and wherein the covert marking pigment is applied to one of thetwo side edges of each covertly marked paper substrate sheet, andwherein the IR pigment sensor of step (b) scans the side edges of eachof the paper substrate sheets of step (a).
 24. The process of claim 21,wherein the covert marking pigment incorporated into the paper substratesheets of step (a) has a particle size in range of from about 0.5 toabout 1.5 microns and is in an IR detectable amount of from about 2 toabout 10 mg/m².
 25. The process of claim 21, wherein the IR anti-Stokesshift pigments of step (a) are selected from one or more of: yttriumoxide; sodium yttrium fluoride; lanthanum oxide; Gadolinium (Gd2O2S); orYtterbium (Yb).
 26. The process of claim 21, wherein the covert markingpigment is distributed randomly in the paper substrate sheets of step(a).
 27. The process of claim 21, wherein the paper substrate sheets ofstep (a) are formed into a ream of paper substrate sheets, and whereinfrom one in three to from one in five paper substrate sheets in the reamare covertly marked paper substrate sheets.
 28. A process fordetermining whether or not a paper substrate sheet is an authenticdocument, the process comprising the following steps: (a) providing apaper substrate sheet; and (b) scanning the paper substrate sheet withan IR pigment sensor to detect whether the paper substrate sheetincorporates a specified covert marking pigment, the covert markingpigment being one or more IR anti-Stokes shift pigments selected fromone or more of: yttrium oxide; sodium yttrium fluoride; lanthanum oxide;lanthanum fluoride; yttrium oxysulfide; lanthanum oxysulfide; Gadolinium(Gd2O2S); Ytterbium (Yb); or mixtures thereof; wherein if the IR pigmentsensor detects that the paper substrate sheet: (i) does incorporate thespecified covert marking pigment, the paper substrate sheet isidentified as authentic; or (ii) does not incorporate the specifiedcovert marking pigment, the paper substrate sheet is identified ascounterfeit.
 29. The process of claim 28, wherein each paper substratesheet of step (a) has two outer surfaces, and wherein each papersubstrate sheet which is an authentic document incorporates thespecified covert marking pigment into the paper substrate sheet belowthe two outer surfaces.
 30. The process of claim 28, wherein the covertmarking pigment is distributed randomly in the paper substrate sheets ofstep (a).
 31. The process of claim 28, wherein the IR anti-Stokes shiftpigments of step (a) are selected from one or more of: yttrium oxide;sodium yttrium fluoride; lanthanum oxide; Gadolinium (Gd2O2S); orYtterbium (Yb).